The Wario Land franchise began in 1994 with Wario Land: Super Mario Land 3 on the Game Boy. The game was actually a spin-off of Super Mario Land 2: 6 Golden Coins, which had been Wario's first appearance (in which he was an enemy character). The franchise has since continued with
Virtual Boy Wario Land, Wario Land II, Wario Land 3,Wario Land 4, and Wario Land: Shake It!. Most of the games have been well-received for their unique mechanics, colorful graphics, and comedic atmosphere.
The plot of the games generally involves Wario discovering the existence some massive treasure, and then going on a quest to collect it.
The biggest gameplay feature of most of the Wario Land games is the fact that Wario can use his environment and enemies to "transform" into other things, such as a zombie, a vampire, caught on fire, rolling in a ball, etc. Instead of dying, hitting some enemies gives him temporary "power-ups," which can help the player either progress or find secrets hidden in the level. This also gives Wario a sense of invincibility (except for pits, naturally).
The first game that differed from this style was Wario Land 4 on the Game Boy Advance. Instead, Wario has a heart meter, so he can die by hitting enemies, but there are also some stationary enemies that give him power-ups. Wario Land: Shake It! was similar to this style of gameplay, and included new innovations (such as the titular shaking of the Wii Remote).